Number of water molecules mediating interaction between residues with opposite or like charges across the interface.

sc and mc correspond to the side chain and the main chain, respectively. All the possible pairs of hydrogen bond interactions are considered (so that a given water molecule can contribute to more than one category of interactions). As such the total number of cases under Inter_H and Inter_C (501 and 338) exceeds the number (334 and 217) given in Table 3.